Skeletal evidence of nonritual interpersonal trauma in the central Illinois valley is currently limited to the terminal prehistoric period in the region. Sixteen percent of the entire Norris Farms Oneota skeletal sample died violently, presumably because they intruded upon small groups of Mississippians who had not yet abandoned the region. Archaeological evidence of palisades, however, suggests that the region was embroiled in conflict before the Oneota arrived though the skeletal evidence supporting more than ritualized or geographically sporadic cases of scalping or embedded projectiles has been elusive. This study examines the frequency and nature of interpersonal trauma at Orendorf, a Middle Mississippian (AD 1150–1250) site at the northern periphery of the region. Nine percent (N = 25) of all 268 individuals documented at Orendorf suffered warfare-related trauma, including 13 cases of scalping, six instances of decapitation, five individuals with healed cranial blunt force trauma, three projectile point impacts, and eight cases of projectile injuries inferred by the burial context. All of the traumatized individuals were at or above the age of 15 years and males and females were victimized equally. The trauma rate among adults is 16%, which is less than that of the Norris Farms Oneota (34%) but higher than other Mississippian groups in the Southeast. The nature of the injuries is more consistent with attacks by outsiders than codified or ritualized intragroup violence. Am J Phys Anthropol, 2008. © 2008 Wiley-Liss, Inc.